The CSF is produced by the choroid plexus that is located within the encephalic ventricles. Normal CSF production rate in an adult is 20 ml/hour (or 500 ml/day). The total CSF volume in an adult is 120 to 150 ml. Hence, in normal circumstances CSF is recycled over three times each day. CSF comprises of water (99%), proteins (<0.4 g/l), glucose (0.5 g/l), and chloride (115 mEq/l). Intracranial pressure (ICP) is measured in millimeters of mercury (mmHg) and, at rest, is normally less than 10-15 mmHg.
The ventricular system is a set of structures in the brain continuous with the central canal of the spinal cord. There are four cerebral ventricles: the paired lateral ventricles, and midline the third and fourth ventricles. The lateral ventricles both communicate via the interventricular foramina of Monro with the third ventricle, found centrally within the diencephalon. The third ventricle communicates via the cerebral aqueduct of Sylvius, located within the midbrain, with the fourth ventricle. The three foramina (foramen of Magendie and Lushka's foramina) open to the subarachnoid space. Each ventricle contains a choroid plexus that produces cerebrospinal fluid (CSF) used to bathe, cushion, protect, nourish and cleanse the brain and spinal cord within their bony confines.
CSF flows from the lateral ventricles via the foramina of Monro into the third ventricle, and then the fourth ventricle via the cerebral aqueduct in the brainstem. From there it can pass into the central canal of the spinal cord or into the cisterns of the subarachnoid space via three small foramina: the central foramen of Magendie and the two lateral foramina of Luschka. The fluid then flows around the superior sagittal sinus to be reabsorbed via the arachnoid villi into the venous system. CSF within the spinal cord can flow all the way down to the lumbar cistern at the end of the cord around the cauda equina where lumbar punctures are performed. Hydrocephalus occurs when the fluid cannot flow freely throughout the ventricles and the central nervous system due to various forms of blockage. Except in very rare cases, it is a life-long condition that can only be controlled, not cured, through surgical intervention.
Hydrocephalus
In the physiopathological definition of hydrocephalus, it is an active distension of the ventricular system of the brain resulting from inadequate passage of cerebrospinal fluid from its point of production within the cerebral ventricles to its point of absorption into the systemic circulation.
Causes:
There are two main types of hydrocephalus: congenital or acquired. The former means that the problem existed at birth, although it may not noticeably manifest itself until later in life, perhaps even adulthood. The latter means that the root cause of the hydrocephalus, whether it is head trauma, tumor or infection, occurred after birth.
Aqueductal obstruction, or stenosis, is the most common cause of congenital hydrocephalus. The cerebral aqueduct, which conducts CSF from the third to the fourth ventricle, is blocked due to defect, inflammation, tumor or hemorrhage. This forces CSF fluid to back up, thereby causing hydrocephalus.
Neural tube defects occur when the surrounding and supporting structure of the spinal cord, not the spinal cord itself, is defective or not fully developed. This malformation can create a blockage in the opening at the base of the skull, which in turn retards the flow of CSF from the fourth ventricle.
Intra-ventricular hemorrhage occurs most frequently in premature babies whose blood vessels in the brain have not been able to fully develop. Because of this weakness, the vessels can burst, thereby allowing the blood to block or scar the ventricles of the CSF pathways.
Meningitis, whether viral or bacterial in origin, causes inflammation of the membranes surrounding the brain and spinal cord. Scarring of these membranes may restrict the flow of CSF and lead to the onset of hydrocephalus.
In cases where head trauma occurs, blood from ruptured vessels may lead to inflammation and scarring of the brain membranes, or can even block the absorption of CSF into tissue. If these CSF flow restrictions occur, hydrocephalus develops.
Tumors may grow in the brain and compress areas of the ventricular system, or block the CSF pathways thereby restricting the flow of CSF and leading to the onset of hydrocephalus.
Arachnoid Cysts, or cysts made up of CSF-filled arachnoid membrane, may block the CSF pathways and bring on hydrocephalus. This condition is congenital and may occur anywhere in the brain.
In instances of Dandy-Walker Syndrome, a congenital defect, the fourth ventricle is enlarged and its outlets become obstructed. Because the flow of CSF throughout the brain is obstructed, hydrocephalus develops.
Mechanism and Symptoms:
Acute Hydrocephalus: Obstructive, or non-communicating, hydrocephalus occurs when the CSF does not flow properly between or out of the brain ventricles because of an obstruction, such as from a malformation or tumor. Symptoms of increased intracranial pressure may include headaches, vomiting, nausea, papilledema, sleepiness, or coma. Elevated intracranial pressure may result in uncal and/or cerebellar tonsill herniation, with resulting life threatening brain stem compression
Chronic hydrocephalus: Non-obstructive, or communicating, hydrocephalus occurs when the CSF flows out of the brain ventricles and into the spinal canal, but it is not reabsorbed normally by the tissue surrounding the brain and spinal cord. Normal Pressure Hydrocephalus (NPH) is characterized by a triad of symptoms (Hakim triad) of gait instability, urinary incontinence and dementia is a relatively typical manifestation of the distinct entity normal pressure hydrocephalus (NPH).
Diagnosis:
Magnetic Resonance Imaging (MRI) is a non-invasive diagnostic tool that uses radio signals and a magnet to form computer images of the brain, its ventricular system and coverings, and pathological lesions.
Computerized Tomography (CT Scan) is a technique in which tiny beams of x-ray outline the skull, brain, ventricles, and subarachnoid space. In addition to visualizing the size and shape of the ventricles, abnormalities such as tumors, cysts, and other pathology can also be seen.
Controlled Lumbar Drainage is a technique used to externally drain CSF over a period of several days. The test is used to determine if a patient with NPH will improve with shunt placement.
Cisternography is a test requiring injection of a small amount of radioactive material into the CSF. This test differentiates communicating from obstructive hydrocephalus, and determines CSF flow.
Neuropsychological Tests are a series of questions and answers used to determine if there is decrease in brain functioning due to hydrocephalus.
Treatment: CSF Shunting
A shunt is a mechanical system that comprises a proximal catheter placed into a lateral ventricle; a valve for regulating the differential pressure gradient; and a distal catheter. In specific embodiments, the distal catheter is tunneled subcutaneously down and can be directed either into the peritoneal cavity (ventriculo-peritoneal shunt; VPS) or the right atrium of the heart (ventriculo-atrial shunt; VAS).
A Ventriculo-Peritoneal Shunt (VPS) diverts the CSF from the ventricles in the brain to the peritoneal cavity in the abdomen where the fluid is reabsorbed: the distal (or peritoneal) catheter runs from the valve down to the peritoneal cavity.
A Ventriculo-Atrial Shunt (VAS) diverts CSF from the ventricles of the brain into the right atrium of the heart. The distal (or atrial) catheter is placed into a vein in the neck and then carefully advanced into the right atrium of the heart, where the CSF is reabsorbed into the bloodstream.
Complications:
Complications may occur with shunt systems, including mechanical failure, infections, obstructions, and in some cases complications can lead to other problems such as overdraining or underdraining.
The cure of the obstruction and the repair of the system requires surgery which is not without risks. Revision surgery on patients with blocked shunts is occasionally complicated by serious secondary ventricular or intraparenchymal haemorrhage. The bleeding is caused when the choroid plexus is torn by the tip of the catheter as it is withdrawn.
Infections and anaesthetic complications may also occur.
One of the most common complications with shunts is shunt obstruction. Although obstruction or clogging may take place at any point along the shunt, the ventricular end is the most likely involved due to its small apertures. The ventricular tip of known shunts is punched with a series of holes and/or slots in the side of a silicone tubing piece. The CSF flows through these apertures into the lumen of the tubing. When the choroid plexus (which are the CSF secreting structures) or cellular debris (red cells and tumor cells, for example), or other brain tissues, for example, grow into the holes and invade the lumen of the catheter, the shunt is obstructed and surgery is needed to replace the ventricular catheter or attempt to clear its tip of this tissue.
The removal of the obstruction requires surgery that is not without risks. Revision surgery on patients with blocked shunts is occasionally complicated by serious secondary ventricular or intraparenchymal hemorrhage. The bleeding is caused when the choroid plexus is torn by the tip of the catheter as it is withdrawn. Infections and anaesthetic complications may also occur.
A high protein concentration in the CSF can also clog the shunt. It is known that a protein concentration higher than 4 g/l will clog up most of shunt valves.
U.S. Pat. No. 5,531,673 discloses a tubular ventricular catheter having an improved distal open end that reduces the tearing of any choroid plexus or other brain tissue that might grow into the lumen of the catheter. This catheter is also equipped with an electrical signal generator intended to prevent growth of tissue into the lumen. However, this ventricular catheter does not prevent the system downstream, and especially the valve, from clogging by a high protein concentration (hyperproteinorrachy).
In U.S. Patent Publication No. 2006/0235439, it is suggested that the majority of shunt malfunctions result from the obstruction of the distal catheter tip by accumulating particulate matter such as fat or proteinaceous debris. Thus, the proposed implantable device disclosed therein aims at maintaining the patency of the CSF shunt at its distal end (outlet) using mechanical energy to “scrub” the catheter lumen of particulate debris. This is accomplished by housing a source of mechanical energy that induces waveform in the CSF flowing through the peritoneal catheter.
U.S. Pat. No. 5,584,314 discloses a self-cleaning inlet head operable in both draining and back-flushing modes, using a slidable piston, intended to initiate a mechanical shearing action and loosening any occluding matter in the aperture. The mechanical action is followed by an hydraulic flushing action that can permit flushing some proteinaceous debris but certainly not clearing some tissue invasion.
There is therefore a need for a new designed ventricular catheter tip capable of preventing obstruction from tissue invasion but also clogging from protein precipitation or flocculation along the downstream shunt system.